1. Field of the Invention
The present invention relates to a dish antenna, and in particular to a multi-beam-reflector dish antenna, which provides maximum gain from a fixed size according to a method of numerical analysis and synthesis.
2. Description of the Related Art
Satellite communication is gaining importance in this world of real-time digital distribution of audio and video data around the globe. It is known that for the purpose of increasing the data capacity of a satellite system, for example a direct broadcast system (DBS). And the reflector dish antenna system is a popular antenna system applied to satellite communication.
Traditionally, the circular parabolic dish antenna commonly used embodies an equation x^2+y^2=4fz, in which f refers to a focal length of the parabolic dish. A low noise block with integrated feed (LNBF) module is installed on a focal point of the parabolic reflector of the dish antenna for reception and down conversion of the satellite signals. The LNBF module on the focal point receives the satellite signals with extremely high carrier-to-noise ratio(C/N) to raise gain and lower spillover loss and improve quality of received signals. On the other hand, the concentrated character of the focal point on the parabolic dish is strong enough to suppresses signals from unnecessary satellites and generate a considerably lower signal paralleled with the parabolic dish. Furthermore, only by planting more dish antennas to receive other satellite signals for the parabolic dish can get the good performances of all of the satellite signals that we want.
Accordingly, another method provides a dish antenna with several independent LNBF modules for receiving multiple different satellite signals at the same time. The dish antenna with a single compound LNBF module uses less space and costs less, compared to the previous technique. It is also more convenient and practical for users.
Thus, an even more convenient and practical method, saving even more space and cost, is to receive multiple satellite signals by a single compound LNBF module with multiple LMBF modules to achieve the same effect.
The present invention utilizes a theory of physical optics which is referenced to research as follows.
Research Disclosure Vol. 43, NO. 1, “A Generalized Diffraction Synthesis Technique for High Performance Reflector Antenna”, IEEE Trans. On Antennas and Propagation, Dah-Ewih Duan and Yahmat-Samii, January 1995, discloses a steepest decent method (SDM) which is a widely employed procedure for the synthesis of shaped reflectors in contoured beam applications. The SDM is efficient in computational convergence, but highly depends on an initial starting point and could very easily reach a local optimum.